The present invention relates to a pattern recognition system for a hand-written character, in particular, relates to such a system which operates in a real-time on-line condition, and recognizes correctly both a simple character and a complicated character having both straight strokes and curved strokes, even when each of the strokes of the character are written in the wrong order.
There have been proposed many systems as an on-line pattern recognition system. The U.S. patent application Ser. No. 98,813 filed Nov. 30, 1979 and assigned to the assignee of the present application is one of them, and comprises a character input unit for providing the coordinates of a plurality of points on the strokes of a written input character, a classification unit for classifying the input characters to the first group having equal to or less than three strokes, and the second group having equal to or more than four strokes, an approximate unit for providing a plurality of feature points to each of strokes, the number of feature points being six for each stroke in the first group of characters and three for each stroke in the second group of characters, a pattern difference calculator for providing the sum of the length between the feature points of the input character and those of the reference characters which are stored in the reference pattern storage, and a minimum difference detector for determining the minimum length among the pattern differences thus calculated. The input character is then recognized to be the same as the reference character which provides said minimum length.
For example, when the input character is the pattern "T" having the horizontal stroke " " and the vertical stroke " ", the first comparison is carried out between the input stroke " " and the reference stroke stored in the reference memory. The comparison is carried out so that a plurality of the coordinates of the input stroke are compared with the corresponding coordinates of the reference stroke, and the result of the first comparison is stored in the memory temporarily. Next, the second comparison is performed between the second input stroke " " and the reference stroke for the second stroke. The result of the first comparison and the result of the second comparison are added to each other, and the sum is stored temporarily. The comparison of the input character is carried out for all the reference characters, and the minimum sum of the comparisons is searched for among the temporary storage. Thus, the reference character "T" provides the minimum sum, then, the input character is recognized as the pattern "T".
Accordingly, if the input character is written in a wrong stroke order, that is to say, when the vertical stroke " " is written first, and the horizontal stroke " " is written secondly, the first input stroke " " will be compared with the stroke " " of the reference character, and the second input stroke " " will be compared with the stroke " " of the reference character, the sum of the comparison or the pattern difference between the input character and the reference character will be very large. Thus, the input character would be recognized wrong.
Although there is less opportunity of wrong writing order in an alphabetical character, there is much possibility of the same in a complicated Chinese character and/or a Japanese character, and the wrong order of the writing would make the pattern recognition almost impossible in a prior art.